Magnetic Effects Of Current Question 449

Question: The figure shows two infinite semi-cylindrical shells: shell-1 and shell-2. Shell-1 carries current $ i_{1} $ , in inward direction normal to the plane of paper, while shell-2 carries same current $ i_{1} $ , in opposite direction. A long straight conductor lying along the common axis of the shells is carrying current $ i_{2} $ in direction same as that of current in shell-1. Force per unit length on the wire is

Options:

A) zero

B) $ \frac{{\mu_{0}}i_{1}i_{2}}{2\pi r} $

C) $ \frac{2{\mu_{0}}i_{1}i_{2}}{\pi r} $

D) $ \frac{2{\mu_{0}}i_{1}i_{2}}{{{\pi }^{2}}r} $

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Answer:

Correct Answer: D

Solution:

[d] Magnetic field at the centre of the shell $ =2\frac{{\mu_{0}}i1}{{{\pi }^{2}}r} $ Force per unit length of the wire $ F=Bi_{2}\times 1 $ $ =[ 2\frac{{\mu_{0}}i_{1}i_{2}}{{{\pi }^{2}}r} ] $